Conventional memory modules may comprise a plurality of memory cells or devices having termination resistors connected thereto. In this regard, when a termination resistance value of a termination resistor is connected to a bus for transmitting a signal, the signal may vary according to a configuration of the termination resistor, a resistance value of the termination resistor, and a connection status of one or more other memory modules. As a result, a swing range of the signal may also vary, and therefore, it may be necessary to change a value of a reference voltage for determining the logic state of the signal.